Where fluid pressurising stations are provided between the upstream and downstream portions of a conveyor pipeline, it is preferred that the capsules should remain in the pipeline as they pass through the fluid pressurising station and that they should progress continuously through the fluid pressurising station.
This is achieved by providing fluid pressurising stations, for a pipeline conveyor in which load-carrying capsules are conveyed along a pipeline by means of a fluid flowing along the pipeline, comprising a transfer conduit having upstream and downstream ends respectively connectable to upstream and downstream portions of the pipeline for the passage of load-carrying capsules; outlet and inlet conduits respectively connected to the upstream and downstream ends of the transfer conduit to allow fluid to flow from the upstream portion of the pipeline and to allow pressurised fluid to be fed into the downstream portion of the pipeline; an inlet port interconnecting the inlet conduit and the downstream end of the transfer conduit and having upstream and downstream edges at the intersection between the inlet conduit and the downstream end of the transfer conduit; an outlet port interconnecting the outlet conduit and the upstream end of the transfer conduit and having upstream and downstream edges at the intersection between the outlet conduit and the upstream end of the transfer conduit; and valve means mounted in the transfer conduit for pivotal movement about an axis extending transversely of the transfer conduit at or adjacent the upstream edge of the inlet port.
Fluid pressurising stations such as this, for transporting load-carrying capsules by means of a pneumatic fluid flow, are described in the specifications of British Patent Specification No. 1 436 983 granted to the British Hydromechanics Research Association and U.S. Pat. No. 4,017,039 in the name of Georgia Tech. and, in these cases, the outlet and inlet conduits are respectively connected to the inlet and outlet ports of a fan so that air withdrawn from an upstream portion of the pipeline is pressurised by the fan and then re-introduced into a downstream portion of the pipeline. In both arrangements, motion of capsules along the pipeline and into the transfer conduit causes a build-up in pressure in the air between the capsule and the valve member and this increase in pressure causes the valve member to rotate about its pivotal axis so as to allow the passage of the capsule through the transfer conduit and into the downstream portion of the pipeline.
While these arrangements operate reasonably satisfactorily for fast moving capsules and for capsules which prevent pressurised fluid in front of the capsules from escaping too readily through the clearance between the capsules and the pipeline, because the valve member is pivoted out of the path of the capsule by means of pressure built up ahead of a capsule, it is clear that operation of the valve member can only take place at the expense of retardation of the capsule in its motion through the pressurising station. Moreover, if the pressure downstream of the valve member is sufficiently high, the pressure built up ahead of the capsule will be insufficient to open the valve member.
Difficulty is also encountered on some occasions when the capsules are not travelling at high speed as, for example, when restarting a capsule from rest. In this situation, the build-up of fluid pressure between the capsule and the valve member is not sufficient to cause the valve member to pivot out of the path of the capsule and capsules make frequent contact with the valve member. These impacts cause damage both to the capsules and to the valve member.
It has also been found that, when the valve member has been deflected out of the path of the capsules, it restricts the flow of fluid through the inlet port into the downstream portion of the pipeline, thus imposing intermittent excessive loading on the fluid pressurising means. This results either in loss of efficiency of the pressurising means or intermittent retardation of the fluid flow so that when the valve member is returned to its closed position there is an appreciable lag while the fluid flowing into the downstream portion of the pipeline accelerates back to its normal steady state and this restriction of flow causes a downward force on the valve member which may cause it to contact the capsule passing underneath it.